Without vitamins in our diet we wouldn’t survive but taking too many can be harmful. There’s a limit to how much we actually need.

However, since the discovery of vitamins - or “vital amines” as they were originally dubbed in 1912 - the idea that more is better has been promoted, much to the benefit of manufacturers in a billion pound industry.

Driven by health-conscious people, and some scepticism of mainstream medicine, the worldwide market is huge. Vitamin supplements don’t have to meet the restrictions of “synthetic” drugs, so special licenses are not needed to sell them.

One driving force behind the high doses of vitamins many of us now take came from the support of two-time Nobel prize winner Linus Pauling. In the 1970s, he strongly promoted the work of American biochemist Irwin Stone, who said that very high amounts of vitamin C could be used to treat the common cold and even cancer.

Despite the excitement - and our continuing belief that high doses of vitamin C will cure our colds (for example by taking the 793% recommended daily amount in a Berroca tablet) - the cold hand of scientific trial has laid this idea to rest. Several rigorous trials have showed little effect of vitamin C as a palliative agent that will relieve symptoms of the common cold or more seriously, cancer.

More cases of cancer not less

Worse still, for a number of years the anti-oxidant properties of vitamin C, vitamin E and the beta-carotene form of vitamin A (commonly found in carrots) were considered to make them anti-cancer agents. A series of clinical trials later, and it seems that they either have no effect or can actually raise the incidence of cancer. Vitamin E supplements were not found to reduce prostate cancer, but instead led to a statistically significant increase of the disease. The increase was also evident in long-term follow ups of patients, suggesting that detrimental effects can continue after treatment has finished.

A study of vitamin E and beta-carotene found that these didn’t reduce the incidence of lung cancer, with beta-carotene actually increasing death rates from lung cancer and heart disease. Similar findings were found with beta-carotene combined with vitamin A. Unfortunately more recent studies don’t paint a better picture; the use of dietary vitamin and mineral supplements in older women increased their risk of dying.

The conclusions then for the use of vitamin supplements to prolong life seem rather grim.

Some anti-oxidants are bad in high doses

The aim of these trials was to look at whether taking more vitamins was a good thing. But the question may have been answered by looking a bit more closely at how these vitamins actually work. Take beta-carotene for example. It’s an anti-oxidant and suggested by some to prevent cancer and help with the effects of ageing, but it can be broken down in the body into a molecule that interferes with the body’s own system that prevents cancer.

Beta-carotene is part of the vitamin A family which controls many systems of the body. Vitamin A is converted in the body to retinoic acid which is an instruction molecule; it binds to proteins (receptors) that instruct cells to stop dividing, the underlying basis for uncontrolled cancer growth.

It’s ironic then that beta-carotene can be broken down in the body into particular chemicals that block the action of retinoic acid on its receptor, and therefore an essential system in the body that protects against cancer. This may override the beneficial anti-oxidant properties of beta-carotene and explain why beta-carotene at the wrong high dose can be harmful.

We need to know much more about how vitamins work and the biochemical consequences of high doses - especially as we take so many without thinking they do us harm. A better and more complete understanding of vitamins could help us find a mix that is beneficial for disease.

Vitamin supplements have saved millions from death or disease in countries where there is a deficiency in these essential nutrients. And new discoveries are showing that nutrients such as vitamin A are having unexpected roles in the brain and may be essential for processes necessary for learning and memory.

But we still need to know how to get the benefits right in countries that are vitamin rich.Until we get this right, my advice would be to get all your vitamins and nutrients from a balanced diet that includes fruit and vegetables.

The billions of pounds spent on vitamin supplements are wasted in the western world and it is a crime that the supplements are not redirected to the countries that could actually use them.